After being detained he received medical treatment but astonishingly was found to be unharmed.

Hawaiian Airlines spokesman Alison Croyle said airline staff noticed the boy on the ramp after the flight arrived and immediately notified airport security.

"Our primary concern now is for the well-being of the boy, who is exceptionally lucky to have survived," she said.

Aviation expert Peter Forman said he was shocked the teenager managed to survive.

He said: "The odds of a person surviving that long of a flight at that altitude are very remote, actually.

"I mean, you are talking about altitudes that are well above the altitude of Mount Everest.

"And temperatures that can reach 40 degrees below zero."

"A lot of people would only have useful consciousness for a minute or two at that altitude.

"For somebody to survive multiple hours with that lack of oxygen and that cold is just miraculous. I've never heard of anything like that before."

Rosemary Barnes, a spokeswoman at the San Jose airport, said the FBI and Transportation Security Administration were investigating how the teen breached security and made it onto the plane.

Heat from hydraulic lines in the wheel well along with retained heat in the tyres could have helped keep the stowaway warm, America's Federal Aviation Administration reported.

In addition, a plane's steady climb to high altitudes can allow passengers to drift into an unconscious state as oxygen becomes scarce.

As the heat cools from the wheel well, a stowaway can develop hypothermia, a condition that help preserves their central nervous system keeping them alive.

Both hypoxia and hypothermia may resolve as the plane gradually descends for landing, the administration added.

Others stowing away in wheel wells have died, including a 16-year-old killed after stowing away aboard a flight from Charlotte, N.C., to Boston in 2010 and a man who fell on to a London street from a flight from Angola in 2012.